1. Field of the Invention
This invention relates generally to tape cassettes, and more particularly is directed to improvements in tape cassettes of the type in which a magnetic tape is merely wound on cylindrical circumferential surfaces of hubs rotatable within the housing and which do not have flanges for guiding the tape wound thereon.
2. Description of the Prior Art
In general, when a cassette-type recording and reproducing apparatus is changed-over between its fast-forward operating mode and its record or playback operating mode in which the tape is advanced at a normal forward speed, slack is likely to develop in the tape between the hubs occupying the supply and take-up positions in the cassette disposed at the play position. Such slack results from the fact that the tape is wound more tightly on the hub in the take-up position during advancement of the tape at the normal forward speed, as in the record or playback operating mode than during high speed advancement of the tape, as in the fast-forward operating mode.
In existing tape cassettes of the type in which the tape is simply wound on rotatable hubs within the cassette housing, that is, in which no flanges extend radially from the hubs for guiding the tape as the latter is being wound or unwound, lubricating sheets are usually provided against the inner surfaces of the housing walls for reducing the frictional resistance to turning of the hubs with the tape wound thereon. If the cassette housing is dimensioned so that the lubricating sheets therein closely engage and guide the opposite side edges of the tape as the latter is being wound on the hubs, it is likely that, during a recording or playback operation following a fast-forward operation, the loosely wound turns of the tape on the hub in the take-up position will be seized by the lubricating sheets to resist further winding of the tape on the take-up hub even though the tape is being continuously advanced thereto by the capstan and pinch roller. Accordingly, the tape will become slack or loose between the nip of the capstan with the pinch roller and the take-up hub with the result that a tape loop may be formed and caught again between the capstan and pinch roller so as to be eventually wound around the latter and cause the tape to be severed or seriously damaged.
If the distance between the top and bottom walls of the cassette housing is selected to provide a significant clearance between the tape wound on the hubs and the lubricating sheets disposed against the inner surfaces of the housing walls, then the tape can shift in the axial direction relative to the hubs when being wound on the latter, particularly upon repeated change-over between the fast-forward operating mode and the record or playback operating modes, with the result that the side surfaces of the tape coiled or wound on each hub will be stepped or wavy. Such stepped or wavy side surfaces of the wound tape are again engageable by the lubricating sheets to resist winding of the tape on the hub in response to turning of the latter, particularly at a time following a period of fast-forward operation in which the tape is only loosely wound on the hub.
In order to overcome the foregoing problems, it has been proposed to form the lubricating sheets with numerous raised beads or ridges engageable with the axially facing surfaces of the hubs and also the edges of the tape wound thereon. Although it had been expected that the raised beads or ridges would ensure the accurate or smooth winding of the tape on each hub while avoiding seizing of the wound tape between the lubricating sheets, the results in practice have not lived up to such expectations. More particularly, since axially facing surfaces of the hubs are engaged, under significant pressure, with raised beads or ridges on the lubricating sheets, the precision of the axial location of the hubs thereby is unstable or deteriorates with use due to the resilience or deformation of the raised beads or ridges. Therefore, after more or less extended use of a cassette, the hubs therein are no longer precisely located in the axial direction and uneven winding of the tape can again occur with the previously described undesirable results.